The use of vehicles to carry out terror atrocities across Europe has forced the security services to rethink their counter-terrorism strategy.

Stockholm, where a radicalised, determined killer used a truck to bring carnage to the city streets, has grimly highlighted how difficult it is to defend against low-tech terror.

What will have particularly worried Western security officials was that Rakhmat Akilov, 39, an asylum seeker from Uzbekistan, had also managed to turn his vehicle into a moving bomb.

Had the home-made explosive device detonated, the death toll would have been much higher.

Security chiefs have long feared a shift from sophisticated terror plots, popular with al Qaeda, to attacks carried out by lone wolves making use of weapons from whatever is at hand.

It means the often slow build up to an attack, which has proved vital in providing intelligence warnings of such plots, is no longer available.

The Stockholm attack took place less than a fortnight after a similar atrocity carried out by Khalid Masood, who drove a car into pedestrians on Westminster Bridge and then stabbed to death a policeman at the Houses of Parliament.

And on the day after the Westminster attack, Belgian security agencies responded to what they described as a possible terror incident after a man drove a car towards pedestrians in the Belgian capital Antwerp.

These attacks have placed front-line counter-terrorism units across Europe on high alert.